"Scale oriented" embedded modeling of the North-Western Mediterranean in the frame of MFSTEP

[摘要] An embedded forecasting system was developed for the North-WesternMediterranean at 3-km resolution. The system is based on the Symphoniehydrodynamic free surface model and on the variational initialization andforcing platform VIFOP. The regional model is initialized and forced at itsopen lateral boundaries by the MFS GCM and forced at the surface by theALADIN numerical weather prediction model. Once a week, a five-day forecastis produced after a hindcast of seven days. This pre-modeling period of7 days before beginning the forecast allows the development of the smallscale features associated to the high resolution. The relevance of the 5-dayforecast strategy has been examined by comparing the forecasted fields tohindcast fields (forced by meteorological and oceanic analyses) considered asa reference. Mismatches remain at a very low level indicating a good qualityof the forecasted forcing fields and also possibly to the strong windconditions which prevailed during the period. The embedded forecasts havebeen compared to the MFS observing system (SST and MedArgo) during 6 forecastcycles between September 2004 and February 2005. It was basically found thatin the North-Western Mediterranean, the MFS basin-scale model and thus theregional model forecasts are characterized by large negative biases ofsalinity in the first 100 m under the surface leading thus to too lightsubsurface waters. The underestimation of temperature by the regional modeljust below the surface and its overestimation at 30m deep can be attributedto an overestimation of the turbulent mixing. The regional model allows torepresent a number of processes especially those induced by the wind ascoastal upwelling under stratified conditions, dense water formation over theGulf of Lion shelf, deep mixing in the convection zone or influence on theNorthern Current penetration in the Gulf of Lion.

[学科分类] 海洋学与技术